1. Field of the Invention
The present invention relates to a precision roll turning lathe, and more particularly to a precision roll turning lathe for use in machining of a roll mold for extrusion molding of an optical product, such as a lens sheet.
2. Background Art
A roll turning lathe is among machine tools for machining rolls. A roll turning lathe is a lathe in which a tool post, having e.g. diamond tools attached thereto, is mounted in a carriage, and is basically used for machining circumferential grooves in a roll by rotating the roll with a headstock and feeding the carriage in the lateral direction (X-axis direction) of the roll. When machining axial grooves in a roll, the carriage is fed in the longitudinal direction (Z-axis direction) of the roll while indexing the roll with the headstock (C axis), thereby producing the axial grooves.
The recent advancement of machine control technology has realized ultraprecision machining with a roll turning lathe. These days roll turning lathes are used to machine molds for molding of optical lenses. The applicant has proposed precision roll turning lathes which enable such ultraprecision machining (Japanese Patent Application Nos. 2006-130066, 2006-135560, 2006-156388, 2006-165144 and 2006-166404).
These precision roll turning lathes enable machining of ultraprecision roll molds for use in extrusion molding of a lenticular lens sheet, a cross lenticular lens sheet, a prism sheet, etc. which are used in a backlight of a liquid crystal panel. Ultraprecision machining of a roll mold by means of such a roll turning lathe involves the problem that it takes a long time to complete machining of one roll. With the recent progress toward larger-sized liquid crystal displays, roll molds are also becoming larger. For instance, there is a case where a roll mold for a lens sheet, having a length of even two meters, is machined with a roll turning lathe.
No long time is needed to machine one groove in a roll. In the case of the above roll, it takes only about one minute to machine one longitudinal groove in the axial direction. However, it is a characteristic feature of a roll mold for a lens that because of the fineness of one groove, vast numbers of grooves must be machined as a whole. Assuming that 30,000 longitudinal (axial) grooves are to be machined in a roll, it will take about 30,000 minutes, i.e. 500 hours, or 3 weeks to machine all the grooves in the roll without interruptions.
In order to solve the problem, study has been made by the applicant on the use of an air slide apparatus, mounted on a tool post of a roll turning lathe, for high-speed linear movement of a cutting tool in the longitudinal direction of a roll.
When an air slide apparatus is used in precision machining of a roll, how to supply air and electric power to an air slider is a problem. A method, commonly used for an air slider, is to supply air and electric power by means of a cable chain which bends with a movement of the air slider. This method, however, has the drawback that the air slider can vibrate when the cable chain deforms, leading to a lowering of machining precision.
An air slider may vibrate also due to inertia force at the moment the air slider starts to move or comes to a stop or at the moment it changes direction. The vibration will significantly lower machining precision. This also has emerged as a problem to be solved.